The Spinal Motion Segment
There are thirty-three vertebrae that make up the human spine. Between each one is a spinal motion segment, also known as a functional spinal unit. Spinal motion segments are made up of:
- Two vertebrae
- Intervertebral disc
- Two facet joints
- A host of supportive ligaments and other soft tissue
The first three in the bulleted list make up what is known as the articular triad, because they allow for the minute articulation between vertebrae. The main role of the spinal motion segment is to allow for motion of the upper body while maintaining enough structural integrity to stabilize the spine and prevent injury to spinal nerves that exit at each level of the spine.